The present invention relates to extraction towers for sugar beet cossettes. Such towers comprise a hollow cylinder forming an upright tower housing. The inner wall of the housing may be provided with baffles. Concentrically in the housing there is arranged a conveyor shaft for rotation in the housing and for transporting the cossettes upwardly through the tower by means of conveyor or transport wings. The lower end of the conveyor shaft is equipped with cossettes distributing means adjacent to the bottom of the tower housing. Feed means are arranged to supply a mixture of cossettes and juice into the lower end of the tower and juice extraction means are also connected to the lower end of the tower. Cossettes discharge means are arranged at the upper end of the tower for removing the leached cossettes from the tower. Further, leaching liquid supply means are also arranged at the upper ends of the tower.
Extraction towers of the just described type have been constructed in the past for ever increasing throughput capacities calling respectively for ever increasing dimensions. However, such increasing dimensions result in problems regarding the uniform distribution of the cossettes as well as of the flow of the juice in the bottom area of the tower. It has been found, that such problems cannot be properly solved by the prior art feed-in devices for the cossettes and by the juice extraction devices known heretofore.
It has been customary heretofore for a long time to supply the sugar beet cossettes into the lower tower area near the bottom of the tower through an opening in the vertical tower housing adjacent to the bottom thereof. This may be accomplished through supply conduit means directly connected to the bottom area of the tower housing through the lateral wall thereof. Another way of accomplishing this feed supply is disclosed in German Patent Publication (DOS) No. 2,106,464, wherein a screening feed screw is employed for this purpose. However, where large tower diameters are involved, it is to be expected and hardly avoidable that inside the tower directly adjacent to the inlet port cossettes accumulate at least temporarily. Such accumulation of cossettes will be distributed only when the cossettes distributing device rotating with the conveyor shaft enters into and passes through the area of cossettes accumulation. The proper leaching and juice extraction is at least impeded during such accumulation of cossettes since the intense cossettes liquid contact does not take place in such accumulations, whereby the total extraction time is prolonged and the total length of the contact path between cossettes and leaching liquid is reduced.
German Patent Publication (DAS) No. 1,003,660 suggests to construct the cossettes feed-in mechanism as a screening conveyor screw arranged below the tower bottom as an extension of the rotational axis of the conveyor shaft of the tower. However, this suggestion cannot be realized in practice because the area in which the cossettes juice mixture would have to be fed into the tower by the screening conveyor screw, is taken up by the guide bearing of the transport shaft. Further, the transport or conveyor shaft in extraction towers of large dimensions also take up a substantial space and thus would substantially overlap the outer diameter zone of the screening feed screw in the radial direction. Even if this problem could be solved, the result would still not be a uniform feeding of the mixture of sugar beet cossettes and juice into the tower because the supply of the mixture into the tower would take place radially inwardly adjacent to the outer diameter area of the conveyor shaft, whereby again an accumulation of cossettes, even if it is only temporary, could not be avoided. The mere difference would be, that the accumulation which in the above described German Patent Publication No. 2,106,464 takes place in the area adjacent to the outer housing walls, has been shifted to an inner or central area adjacent to the conveyor shaft of the tower.
German Patent Publication No. H 11,005 discloses a feed supply device which supplies the mixture of cossettes and juice into the tower at the bottom thereof in such a manner that the mixture is uniformly distributed over the whole radial area of the tower. However, this type of prior art device is suitable only for extraction towers with limited dimensions. Thus, this type of device cannot be used in an economical manner in extraction towers of large and largest or maximum dimensions. This is so because in the apparatus of German Patent Publication No. H 11,005 the feed-in takes place through the conveyor shaft. For this purpose, a cossettes distributor arm is secured to the lower end of the conveyor shaft. A conduit supplies the mixture of cossettes and juice to the rear side of the distributor arm which rotates with the conveyor shaft. However, with the increasing dimensions of a diffusion tower, the cross sectional areas required for the transport of the cossette juice mixture also become larger and larger, which poses substantial problems for the construction of a liquid-tight, rotatable coupling for the feed supply pipe. Further problems are encountered in designing the cross sectional area of the cossettes distributor arm because with the increasing surface area of the distributor arm, there also increases the resistance against the movement of this arm through the tower as well as its displacement effect which occurs during the rotation of the distributor arm within the cossette juice mixture in the tower bottom area.